For acquiring the arterial response to the pulsating blood flow by non-invasive blood pressure measurement with a cuff, a pressurizing unit and bleeding valves, there have been the following available methods: displaying only the intensity level of the Korotkoff's sounds graphically by using a microphone, and displaying the cuff's oscillating pressure wave whose constant bleeding rate is filtered out.
However, there do not exist blood pressure measurement devices which display, in real time, information on the response to the pulsating blood flow and the bleeding of the cuff's pressure while simultaneously displaying the simulated mercury and aneroid manometers.
The invention resolves the following problems of prior measurement devices. Using current methods with a microphone, the acquired dynamic response of an artery to pulsating blood flow does not include information on arterial wall motion. That undetected motion includes movement that creates and annihilates the Korotkoff's sounds, movement immediately before and after the sounds, and movement not creating any Korotkoff's sounds.
The response to the pulsating blood flow which is obtained with the AC component of the cuff's pressure after filtering its DC component can show only the trend of the magnitude variation of the cuff's pressure oscillation. But the response can not show the dynamic expansion rate of the arterial wall. Furthermore, the arterial response to pulsating blood flow from which the systolic and the diastolic pressure are determined varies with the environment in which a subject is placed and the individual characteristics of the subject. Obtaining accurate systolic and diastolic readings for various subjects is difficult from judging only the trend of the magnitude of the cuff's pressure oscillation.
A method of acquiring the arterial response to pulsating blood flow is described in Japanese patent applications No. 61-118305 and No. 61-276785. The applications describe a filtering method. The method takes the first derivative of the cuff's pressure and then its integration with respect to time to obtain the increased amount of the cuff's pressure caused by the arterial expansion against the cuff's pressure. Thus it merely increases the accuracy of the filtering of the oscillating pressure. Since this integration is carried on with the first derivatives above a constant threshold value, it is easily affected by a small change in the bleeding rate.
Difficulty often arises in displaying the graphics of the dynamic parameters characterizing the expansion of the arterial wall, namely the displacement velocity of the wall and the parameters related to its acceleration change.
Therefore, with the bleeding rate nearly constant or even changing, this invention acquires the time trend of the artery wall's expansion caused by the pressure fluctuation in pulsating blood flow against the cuff pressure, acquires the wall motion that gives the accurate systolic and diastolic pressure, and monitors the arterial response to the pulsating blood flow.
Another difficulty in non-evasive blood pressure measurements is obtaining the regulated constant bleeding rate and monitoring the change in the bleeding rate over time. In subjects, the detection of Korotkoff's sounds in phases 1, 4 or 5 often becomes difficult, depending on the magnitude of the bleeding rate. Furthermore, the physical and psychological surroundings of a subject alter one's normal systolic and diastolic pressure readings significantly. In these cases, medical personnel using current auscultatory blood pressure measuring methods have difficulty in determining the cause for the changes.
Thus one object of the invention is to resolve the difficulties stated above by displaying in real time the bleeding of the cuff's pressure during the blood pressure measurements as well as displaying the simulated mercury manometer.
A further object of the invention is the measuring and monitoring of the arterial response in nearly real time for those subjects remote from clinics or hospitals.